The preparation of high-activity supported nano-gold catalysts mainly considers two aspects, one is the preparation of nano gold, which ensures high catalytic activity with small size, and the other is the choice of carrier, which should have a relatively large specific surface area and good performance. high wettability and strong interaction with the supported gold nanoparticles and they are highly dispersed on the surface of the carrier.
The influence of the carrier on the catalytic activity of Au nanoparticles is mainly manifested in the specific surface area, wettability of the carrier itself and the degree of interaction between the carrier and the gold nanopowders. A carrier with a large SSA is the prerequisite for the high dispersion of gold particles. The wettability of the carrier determines whether the gold catalyst will aggregate into large gold particles during the calcination process, thereby reducing its catalytic activity. In addition, the interaction strength between the carrier and the Au nanopowders is also a key factor affecting the catalytic activity. The stronger the interaction force between the gold particles and the carrier, the higher the catalytic activity of the gold catalyst.
At present, most of the highly active nano Au catalysts are supported. The existence of the support is not only conducive to the stability of the active gold species, but also plays an important role in promoting the activity of the entire catalyst due to the interaction between the support and the gold nanoparticles.
A large number of research results show that nano-gold has the ability to catalyze a variety of chemical reactions, and is expected to fully or partially replace the existing precious metal catalysts such as Pd and Pt in the fields of fine chemical synthesis and environmental treatment, showing broad application prospects:
1. Selective Oxidation
Selective oxidation of alcohols and aldehydes, epoxidation of olefins, selective oxidation of hydrocarbons, synthesis of H2O2.
2. Hydrogenation reaction
Hydrogenation of olefins; selective hydrogenation of unsaturated aldehydes and ketones; selective hydrogenation of nitrobenzene compounds, the data shows that the Au/SiO2 catalyst with a nano-gold loading of 1% can realize the efficient catalysis of high-purity halogenated aromatic amines hydrogenation synthesis provides a new possibility to solve the problem of dehalogenation by catalytic hydrogenolysis in the current industrial process.
Nano Au catalysts are widely used in biosensors, high-efficiency catalysts, and gold has good chemical stability. It is the most stable among group VIII elements, but gold nanoparticles show excellent catalytic activity due to small size effects, nonlinear optics, etc.
In catalyzing similar reactions, nano gold catalyst has lower reaction temperature and higher selectivity than general metal catalysts, and its low-temperature catalytic activity is high. The catalytic activity at the reaction temperature of 200 °C is much higher than that of the commercial CuO-ZnO-Al2O3 catalyst.
1. CO oxidation reaction
2. Low temperature water gas shift reaction
3. Liquid-phase hydrogenation reaction
4. Liquid-phase oxidation reactions, including ethylene glycol oxidation to produce oxalic acid, and selective oxidation of glucose.